1. Field of the Invention
The present invention relates to a photoelectric converting apparatus which intends to reduce sensor noises.
2. Description of the Related Background Art
As a sensor which is used in a solid state image pickup device or the like, an amplifying type sensor is preferably used to increase an output signal level and the like.
The amplifying type sensor is constructed by a transistor of the MOS type, SIT type, FET type, bipolar type, etc. and charge amplifies or current amplifies the charges accumulated in their control electrodes and outputs from a main electrode. For instance, an example of the amplifying type sensor has been disclosed in Japanese Patent Publication Gazette No. 55-28456. As one of the problems of such amplifying type sensors, a point that the sensor noises are large can be mentioned.
The sensor noises are generally mainly classified into fixed pattern noises (hereinafter, referred to as FPN) which fixedly appear and random noises which are fetched to the control electrode when the control electrode is reset.
Among the sensor noises, since the FPN fixedly appear, they can be completely eliminated by subtracting a dark-state output of the sensor from the photo signal output of the sensor. The dark-state output can be obtained by reading out the output immediately after the accumulation time was set to almost zero, that is, after the sensor was reset.
On the other hand, in order to also eliminate the random noises which were fetched to the control electrode, it is sufficient to subtract the sensor output (photo signal) after completion of the accumulation from the sensor output (sensor noises) just after the start of the accumulation. As such a photoelectric converting apparatus which can execute the subtracting process, there is an apparatus disclosed in Japanese patent application No. 63-47492 which has already been filed by the applicant of the present invention. The above photoelectric converting apparatus has means for storing a photo signal and storage means for storing sensor noises, wherein a difference between the photo signal and the sensor noises which were stored in both of the storage means is obtained.
Although such a photoelectric converting apparatus is very practical when it is used for a line sensor, in the case where it is used for an area sensor, a chip area of the storage means for storing the sensor noises increases. Even if the storage means is provided in the outside of an image pickup device, a field memory or a frame memory is necessary and there is a problem on costs, so that it is difficult to put such an apparatus into practical use.
On the other hand, there is an apparatus in which a photoelectric converting region is laminated to the upper portion of an amplifying transistor in order to increase the sensitivity of the sensor and to relatively reduce an influence by the sensor noises. As such a solid state image pickup apparatus, there is an apparatus disclosed in Japanese patent application No. 1-9089 which has already been filed by the applicant of the present invention.
According to the above solid state image pickup apparatus, if a photoconductive film is laminated, a numerical aperture of the photoelectric converting region is extremely large, so that a sensor output (S) also similarly increases. However, to realize a further higher S/N ratio, it is necessary to reduce sensor noises (N).